the Application of Geochemical, Botanical
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TA/OST 72-13 . THE APPLICATION OF GEOCHEMICAL, _ BOTANICAL, GEOPHYSICAL, AND REMOTE SENSING ! \ MINERAL PROSPECTING TECHNIQUES TO TROPICAL AREAS (State of the Art and Research Priorities) ,.'~ ." j l Office of Science and Technology Agency for International Development Washington. D.C. NOVEMBER 1972 L..-____...J TAjOST 72-13 THE APPLICATION OF GEOCHEMICAL, BOTANICAL, GEOPHYSICAL, AND REMOTE SENSING MINERAL PROSPECTING TECHNIQUES TO TROPICAL AREAS (State of the Art and Research Priorities) ., Office of Science and Technology Agency for International Development November 1972 PREFACE This Report was prepared in connection with the activities of the Planning Group on Science, Technology, and Development established by the Organization for Economic Coooperation and Development. It is intended to serve as a basis for evaluating the current state of the art and research priorities with respect to prospec~ ing for mineral deposits in tropical regions. This activity area was selected for analysis due to (1) its importance in the development context; (2) the relative neglect of research in the area by donor countries and international agencies; and (3) the likelihood that additional research will make major contributions to the solution of critical problems. This Report is based largely on a preliminary analy sis prepared by the U.S. Geological Survey for the Agency for International Development!! and comments subsequently received from numerous reviewers in U.S. Government agencies and universities, other donor countries, and international development institutions. Special apprecia -tion for assistance in reviewing drafts of the Report is extended to the College of Mines, University of Arizona; Geological Survey of Alabama; Agriculture Research Ser vice, U.S. Department of Agriculture; Engineer Agency for Resources Invent-cries, U.S. Department of the Army; Smithsonian Institution; Institute of Geological Sciences, United Kingdom; Resources and Transport Division, United Nations; and the International Bank for Reconstruction and Development. Both conventional and emerging new technologies for mineral prospecting are treated in this paper under the following major topical headings: Geochemical Prospecting, Botanical Prospecting, Geophysical Prospecting, and Remote Sensing. In addition to providing brief descriptions of various instruments and survey methodologies and their principal applications, approximate costs for basic instru mentation as well as for particular types of surveys have 1/ The Appl:!.cat1on of Geochemical, Botanical, Geophys ical, and Remote Sensing Mineral prospectin~ Techniques to Tro ical Areas -- State of the Art an Needed Research; Dorr, J. anH.; Hoover, D. B.; 0 leI, ac ette, H. T.; U.S. Geological Survey (Open File December 1971. been estimated. Bach section concludes with an identifica tion of on-going research activities, research gaps, and priorities with respect to future research. The closing chapter of the Report provides a general discussion of the current capacity and requirements of developing.countries for undertaking mineral prospecting programs. ii 'CONTENTS PREFACE . ABSTRACT 1 ,( INTRODUCTION 3 GEOCHEMICAL PROSPECTING 13 State of the art . 8 Instrument and survey costs 13 Current research •. ... " 15 Research gaps and priorities 16 BOTANICAL PROSPECTING 19 State of the art 19 Botanical prospecting 19 Biogeochemical prospecting 22 Instrument and,survey costs 23 Current research ..... 23 Research gaps and priorities 25 GEOPHYSICAL PROSPECTING 26 State of the art . 27 Induced polarization ., 31 Gravimetry 32 Magnetics . 32 E1ectromagnetics 34 Seismic . ,. 34 ReSistivity 35 Radiometric 35 Other methods 36 Instrument and survey costs 36 iii Page Research gaps and priorities 39 REMOTE SENSING 42 State of the art and current research 43 Visible and near infrared 44 ., Thermal infrared 46 Microwave . 48 Instrument and survey costs 50 Research gaps and priorities 51 CAPACITY OF DEVELOPING COUNTRIES. TO USE RESULTS OF SUCCESSFUL RESEARCH . • 52 SELECTED BIBLIOGRAPHY . • . 56 Geochemical prospecting 56 Botanical prospecting 64 Geophysical prospecting 67 Remote sensing . 70 TABLES Table l.--Comparison of dollars spent on major mLnLng geophysical techniques by agencies in free market nations (in thousands of dollars), 1969 ...........•. ... 28 Table 2.--Summary of geophysical techniques and costs 37 ILLUSTRATIONS Figure l..--Variation in airborne and ground geo physical activity from 1961 to 1968, adapted from Hood and. Kellogg (1969) . 29 Figure 2.--Free-market nation distribution of mining geophysical activity in 1968, from Hood and Kellogg (1969) . • . • . 30 iv ABSTRACT A disproportionate ,percentage of the world's known ore bodies are found in the temperate and, adjacent arid regions of the world. However, there is no geological reason why economic mineral deposits should not be present in the tropical regions of the world in the same relative abundance as elsewhere. The anomalous situation appears to be largely the result of economic and political consider ations which have thus far impeded mineral development in the tropics. Another factor is that many of the classical prospecting techniques have not proved to be nearly as effective in non-temperate regions. In recent years a variety of promising' new' mineral prospecting techniques have been developed in th~ more technologically advanced countries; their potential application in the tropical environment, including the research needed to make them fully applic- able, is the theme of this Report. Geochemical, botanical, geophysical, and remote sen sing techniques of prospecting are in widely differing stages of maturity. Further, marked geophysical differences within the tropical environment impose constraints on various possible applications. As a rule of thumb, the humid tropics present somewhat greater difficulties than the arid tropics, a case in point being the problem of logis tics in the rainforest environment which severely limit ground-based prospecting. Consequently, several airborne reconnaissance methods have great advantages in these situations although the high cost of precise location then becomes a handicap. As a result, research to develop che~per modes of precise location in support of both air borne and ground-based prospecting is needed. Geochemical prospecting is one of the most promlslng methods in tropical environments, although the technique is still immature. The deep weathering, thorough leaching of the soils, and the formation of laterite may hide and i modify anomalous concentrations of sought-for elements and increase the importance of "pathfinder" elements. Research I is needed not only on the mobility and fixation of elements ! ~. \ but also on sampling instrumentation and techniques, still !'" in a rather primitive state in the humid tropics. Ana lytical and data-processing methods have been developed to a high state in the temperate zones, and the techniques can be applied directly to the tropics with little or no modification once the basic problems of sampling media and elemental mobility and fixation have been solved. Geobotanical prospecting in tropical areas is also in an immature stage. Although indications are that this technique may be effective in arid and semi-arid climates, Iittle '~ork has been done in the humid tropics. It is likely -1- ,. that research could make the tool more effective . Many geophysical prospecting methods developed in temperate climates are directly applicable in most tropic environments with little change. Highly conductive surficial zones in the humid tropics, particularly over lateritic soils and laterites, complicate some electrical methods and further research in this field would bring r improved efficiency of interpretation. Geophysical prospecting is the most mature of the techniques cited. Remote sensing is the newest and, except for photo- geologic interpretation, least developed of the techniques which may facilitate mineral prospecting in tropical re gions. It has great potential. Radar mapping in the humid tropics has proved the best way to acquire much basic information rapidly in areas of constant cloud cover; it reveals large-scale features of geology and structure that can be exposed in no other way. The use of multiband spectral imagery and multiband photography holds great promise but is still in a rather rudimentary state; much research is needed and some is being carried on. Photo geologic interpretation is now a highly developed and st~n dard technique where aerial photographs can be secured; lt is, of course, at its best when used in arid regions. Most modern prospecting techniques have lowered the cost of prospecting per unit area, but the capital cost of installing the needed equipment is .substantial, and highly trained personnel are needed. A vast amount of data is sometimes neces'sary to pinpoint the relatively few small areas worthy of detailed physical exploration. In a balanced, integrated survey, several methods should be used in conjunction with each other. Much of the research hitherto accomplished in tropical areas has been done by private companies and is considered proprietary, or by th~ United Nations which is permitted by host countries to publish only a small fraction of its results. The developing countries themselves apply modern exploration techniques to some extent. Basic research by the concerned governmental agencies and rapid publication of results would have beneficial effects for the developing countries as well as